Z-Terra software helps companies visualize sub surface diffractors

Paul Wiseman

Published 6:05 am, Friday, September 27, 2013

With Z-Terra's recent filing of a patent application for "Specularity Gathers for Diffraction Imaging," producers and seismic companies have a new tool for "seeing" what is going on in oil-bearing formations far below the surface. The software takes existing seismic data and from it creates high-resolution imaging of the small-scale fractures in shale reservoirs in order to improve the prospect characterization and pre-drill assessments, according to a press release.

Z-Terra CEO and Chairman Alexander Mihai Popovici explained it as follows: "Diffractions are small discontinuities in the earth. There has been a lot of work done about the mathematics of wave propagations along diffractions."

Diffractions are something that dissipates a wave presented to it. Popovici pointed out that the surface of the B1-B "stealth" bomber works by diffracting radar waves so they do not return to the sender, which would give away the bomber's presence. "We implemented some of these ideas in order to look at discontinuities inside the earth."

One of the features of most interest is the fracture fields in some of the unconventional shale reservoirs. In those, producers "want to see what areas in the earth have higher fracture densities, because these are the areas with higher production," Popovici said.

Currently, he said, smaller operators drill their holdings on a grid in order to try to take advantage of what the formation holds. They notice, however, that they get very different production from each well in spite of the grid and the fact that all wells appear to be in the same field.

One reason for this, Popovici said, is that the porosity of a shale field varies depending on the number of fractures present at any given location. The more fractures, the more porosity, the more a well produces.

"Diffraction imaging is a way to use seismic data -- which is used anyhow to see the structure -- but instead of looking at the structure, you look at discontinuities, specifically the fractures in rock," he said. This data can help drillers place wells and frac zones.

These discontinuities show up clearly because the areas of reflection have a Fresnel zone and areas of diffraction do not. According to www.princeton.edu, "a Fresnel zone (pronounced fray-NEL), named for physicist Augustin-Jean Fresnel, is one of a (theoretically infinite) number of concentric ellipsoids which define volumes in the radiation pattern of a (usually) circular aperture."

"If you only have one diffractor, such as an area of high-density rock in an area of constant density, you can pinpoint that with very high resolution," Popovici added.

As for the quality of the incoming seismic data, he said the program can work with anything, although it does best with more recent data that is typically of higher resolution, particularly if the data is 3D, because the Fresnel zones happen laterally, but all of it is "still the same physical principle."

Z-Terra's software operates in either of two ways. They can sell it to seismic companies that already have a staff able to interpret this type of data, or a producer can send their seismic data to Z-Terra for processing at the company's Houston office. Popovici said that, if the data has already been pre-processed, Z-Terra can get results back in about a week. If it has not been pre-processed, turnaround time depends on the size of the data. "f i''s 50, 60, up to 100 square miles, it takes us about a month," to process the data and then one more week to detect the diffractions. "If it's 3,000 square miles, it takes longer," he said chuckling.

The program was in development for about three years, when some academics from Europe who had done some calculations came to Z-Terra needing someone who could field-test the ideas. Popovici was at first skeptical, not yet realizing the program's uniqueness. When a Z-Terra client, Saudi Aramco, volunteered to pay for the field test, Popovici was more amenable to the project.

As the project went into the field, "We got some surprisingly interesting results," he said, including other information that applies to fractures in carbonate-laden fields such as in Saudi Arabia. So he was sold.

The company has a number of clients in the Permian Basin, including a major producer and a seismic company.